gvfs-test: Mark Sftp.test_unknown_host as expected failure for now
gvfs-test: Mark Sftp.test_unknown_host as expected failure for now

This does not reliably work everywhere, see
https://bugzilla.gnome.org/show_bug.cgi?id=686006#c38
for how to fix it properly.

halfline/gvfs,xkahn/gvfs-cmis,gicmo/gvfs,xkahn/gvfs-cmis,xkahn/gvfs-cmis,gicmo/gvfs,halfline/gvfs,xkahn/gvfs-cmis,gicmo/gvfs,gicmo/gvfs,halfline/gvfs